Soft touch interior trims for vehicles normally comprise a substrate, a soft touch layer and a decorative skin.
The decorative skin can be a natural skin such as leather or a synthetic skin such as a PVC, TPU or TPE skin.
Synthetic skins are often used in the vehicle interior as decorative covering for the different interior trims such as instrument panels, door panels or pillar trims because this kind of skins allows adapting the interior trims to a wide range of styles for the different vehicle models.
It is because the manufacturing processes of the synthetic skins are capable of making different textures and colors.
It is known several processes for manufacturing this kind of synthetic skins for the vehicle industry. Some examples of these are slush molding or spray molding. The materials normally used in these processes are PVC, TPU, or TPE.
One of the main targets for these conventional synthetic skins is the weight reduction.
One approach to tackle this target is the reduction of the thickness of the synthetic skin. It is particularly relevant in the case of large components such as the instrument panel in which a reduction of a few tenths of millimetres means a significant weight reduction.
However when the thickness of the synthetic skin is too much reduced it arises other problems, particularly an aesthetic problem and a safety problem.
The aesthetic problem it is because a skin with a too much reduced thickness is more susceptible to deteriorate during the manufacturing process of the skin due to its tendency to shrink, and as well, during the manufacturing process of the interior trim due to the usually high temperatures of the material of the soft foam layer. Moreover, a skin with too much reduced thickness is as well more susceptible to deteriorate when the interior trim is in use in the vehicle interior after years of use.
The safety problem is the most important problem of them. This problem is due to the uncontrolled behavior of the synthetic skin when an airbag placed under the interior trim is triggered when the synthetic skin is too thin.
As the synthetic skin comes thinner, its tendency to flow instead of tearing goes greater, losing control on the way the skin tears, and consequently preventing a correct deployment of the airbag.
This problem becomes even worse, when the synthetic skin material is exposed to high temperatures, for instance, in summer time after several hours under the sunshine.
Other approach to tackle the weight saving target is replacing part of the thickness of the external high quality aesthetic synthetic skin by a lighter second layer, placed on its back side, achieving this way a global reduction of the superficial density of the synthetic skin. According to this solution it is known a double layer skin which comprises a high quality decorative front layer with a small thickness and a supporting back layer made of foam. The foam configuration of the back layer allows reducing the density of the total synthetic skin, and consequently reducing its total weight.
One example to illustrate this solution is the German patent DE102013215107.
However in this second case it is demonstrated that the behavior of the synthetic skin when the airbag is triggered is also uncontrolled, because the risk of a poor tearing becomes higher, and consequently the risk of improper airbag deployment and of uncontrolled fly-out of particles becomes higher too.
In this precedent, the second skin layer comprises a non-homogeneous foamed back layer due to the presence of irregular voids, of very different sizes. It results in a second skin layer with lack of homogeneity of its mechanical properties. Consequently, at the time of triggering the airbag, the starting point and the path of the tearing line of the synthetic skin, become unpredictable and uncontrolled.
In view of the disadvantages mentioned above, the object of the invention is a soft touch interior trim for vehicles with a synthetic skin, having a reduced weight, and a good behavior when the airbag placed under the interior trim is triggered, in order to ensure a reliable release of the airbag and at the same time fulfilling the high quality aesthetic requirements usually demanded for this kind of interior parts, even after years of use.